I suppose that this was not done previously because of the lack of clear bottles. Clear plastic bottles did not exist until several years ago. Now they are everywhere. Half the trash on the streets of Ecuador and along the highways are discarded plastic bottles.
In Mexico City, no one drank the water. If you did, you tended to get sick. Amoebic dysentery is a very convincing way of learning this.
The water run underground through an ancient subterranean lake, often through ancient lead pipes in an areas frequently affected by tremors and earthquakes, by which ancient Aztec sewage seeped. Then it was pumped to a tank on top of the roof. Some tanks had a lid on them, others did not. Either way, when you looked inside, the sides had a combination of slimy green and black algae on the sides and bottom. If the pump broke down or was not working, the level of the water in the tank dropped, and green, brown and blackish water came out of the faucet.
This method might work in Cuenca, where no one trusts the water, but it would be inadvisable in Mexico City, because there are a lot of nasty minerals in the water as well as bacteria.
In Quito, the water is safe in most of the city, but a lot of people do not trust it. The rich buy bottled water, the poor boil it. Boiled, it has a rather funny taste. I drank tap water, boiled water and bottled water with no ill effects.